The fighting included ground clashes and airstrikes by Libyan military planes.

Witnesses said pro-Gadhafi forces stormed into the town of Brega on the Gulf of Sirte and briefly seized its oil installations and an airstrip. Opposition fighters say they recaptured both sites. Later, Western media reported loud booms that they linked to at least two bombings from Libyan aircraft.

Video clip: Pro-Gadhafi Forces Attack 2 Eastern Towns

Witnesses say military forces carried out an airstrike in the nearby town of Ajdabiya. Both towns are on the western edge of the region of eastern Libya that is now largely under opposition control.

The fighting occurred on the same day that Gadhafi delivered a televised speech to supporters in Tripoli. He said he could not resign because he holds no political office in a system that he said puts all power in the hands of the people.

However, protesters in the rebel-controlled eastern city of Benghazi called for Gadhafi's resignation. They chanted anti-Gadhafi slogans as they burned copies of the Libyan leader's Green Book. Libya has no formal constitution but Gadhafi often refers to the publication, which outlines his political and economic philosophy for the country.

Separately, anti-government activists in eastern Libya called for United Nations-backed air strikes against pro-Gadhafi forces. Libyan dissidents meeting with U.S. officials in Washington this week made similar calls.

The Libyan Human Rights League estimates at least 6,000 people have died in the two-week old uprising. At a conference in Paris on Wednesday, spokesman Ali Zeidan said about half of the deaths were in Tripoli.

Some information for this report was provided by AFP.

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